Proper Oil for stock 4.0L xj

SO I'm doing a bunch of fluid changes, and I've been using mobil-1 synth 10-30w for about 5 years now in my 1991 5speed sport 4.0HO. I thought maybe I'd look into other oils and ending up spending last two hours reading about how they changed the oil formulas with the zinc levels and all this. All the threads were pretty old though, and I never found a decent conclusion to the debate. So I'm wondering, is the current Mobil 1 syth ok to use? Or what would be the best choice? Also, for the differentials (Dana 30, 8.25, no towing) is royal purple 75-90 ok? Sorry I know this is a raging debate but really just want a simple answer. Thanks y'all- TJ

Standard answer I give,,,, Its a Truck engine,,use truck oil.
10w-30 is the recommended oil for most situations.15w-40 Rotella T has a large following.
A GOOD filter is a must for proper oil pressure at idle and start-up>NO Fram.
Normal oil pressure for a hot engine at idle is 13 psi or >.(10w-30 oil)
I have 4 XJs in the driveway,allover 200,000.They get green jug Castrol 10w-30 or Rotella T 15w-40. Depending on the weather= thinner when its cold
My 96 w/375,000 still carries 20 psi hot idle.

10w30 syn is fine ... I use syn 5w40 (Castrol full Synthetic) up here ... I used to use 10w30 and 15w40 but wanted a quieter motor (lifters) which the 5w40 has delivered so far.

Used to run Dello, but have switched to Valvoline VR1.

Oil is oil, buy whatever is on sale. ZDDP is for high compression high performance motors.

Oils that cost extra, do not provide extra benefits in direct relation to their price.

The oil change interval you follow is more important than the oil used. Every 3-5,000 miles is when I change, using whatever is on sale at the WallyMart or Farm and Fleet store. Clean oil means a happy motor.

I use 15w40 Rotella T (dino), let me tell you why.

1. I live in a subtropic/saltwater environment. Todays forcase is 95F/100% humidity @12ft above sealevel so heat is always an issue. The 10w40 helps deal with the engine heat and keep the oil pressure nice an high even this close to the sun.

2. ZDDP is not going to hurt anything and is actually prefered for flat tappet engines.

3. It all but silinced my valve train chatter.

4. Florida does not hat emissions standards. So in the event that it should mess with my cat (which I highly doubt) I'll just bore it our or cut it out. Which in retrospect would probably make me not notice the noise of the valve train chatter lol!

5. Its affordable

If your using 10w30 synthetic ANYTHING in your rig and it works and you can afford it......the keep on doing it. I agree with Tim, oil change frequency and a quality oil filter are key. What good does it do you to put that fancy dancy oil in your rig thats designed to break crap loose and clean up your motor if your just going to keep recirculating it through a pos filter. I always use an oversized filter. For instance Napa Gold stock #1085 but you can use a 1515. It looks close to twice the size of the 1085. Plus there drain back device is proven. Again what good does it do to put that fancy oil in your rig if your filter is allowing it to dry start. Just my 2cents.

Thanks for al the info. Ya I change my oil regularly and use a good filter. I was just wondering about mobil-1 with the flat tappet engine, is it ok. Maybe I should switch oil makes for my next change, if the mobil-1 is not protecting the engine like some others would. Also, any thoughts on the 75-90w for the dana 30+8.25 combo? thanks again - TJ

Close to the sun at 12 feet? I use rotella 10w30 up here at 5280 and have never had oil pressure issues for what it's worth.

mgeebxj said:

Close to the sun at 12 feet? I use rotella 10w30 up here at 5280 and have never had oil pressure issues for what it's worth.

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Thanks, I appreciate it....lol I'm just being proactive. My pressure is so high now that I corrected all of the overheating issues, I'm going to try stepping down to 10w30 when I'm out of the 15w40.

FUN EXPERIMENT FOR THE CLASS:

Remove one (1) brand new flat-tappet for a 4.0 engine from the box.

Stand the flat-tappet on a sheet of glass that is laying down.

Note how the flat-tappet does not have a flat bottom--it is beveled outward and will rock on the glass.

Record the result: flat-tappets are not flat on the bottom.

Now, find a 4.0 that has some mileage on it that has been run with non-ZDDP oil.

Remove one (1) flat-tappet.

Stand that used flat-tappet on the same glass.

Note that the used tappet is FLAT.

"Back in the day" THIS WAS THE TEST TO SEE IF YOU COULD RE-USE THE TAPPETS IF THE CAM MIC'D OK.

Does the lack of ZDDP in modern engine oils result in additional wear to non-racing/low-compression flat-tappet engines? Why yes, yes it does. Will running modern engine oils that contain no ZDDP DESTROY your 4.0? Not likely. Will running modern engine oils that contain no ZDDP shorten the service life of your 4.0? Yes.

Did Chrysler require the use of a break-in additive HIGH in ZDDP for new 4.0s for the first 500 miles? Yes. If you failed to use the break-in additive would that void the engine warranty? Yes.

Is it against the law to use ZDDP oil in an engine with a catalytic converter? No. Could using ZDDP oil in an engine with a catalytic converter harm the converter? Maybe. Which is cheaper--an engine or a catalytic converter? Converter.

Will new pending EPA regulations mandating E15 fuels in all states result in damage to older vehicles' fuel systems? Yes. Then why does the EPA want ZDDP gone and E15 fuels if they damage older vehicles? Well, they have to get you into electric cars one way or the other!

Joe, you are a conspiracy theorist after my own heart.....and you made several good points!

bugout said:

Joe, you are a conspiracy theorist after my own heart.....and you made several good points!

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Just because I am paranoid does not mean everyone isn't out to get me! :eyes:

Does the lack of ZDDP in modern engine oils result in additional wear to non-racing/low-compression flat-tappet engines? Why yes, yes it does. Will running modern engine oils that contain no ZDDP DESTROY your 4.0? Not likely. Will running modern engine oils that contain no ZDDP shorten the service life of your 4.0? Yes.

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Modern oils do contain ZDDP in reduced amounts as compared to the most oil made 20 years ago.Currently the ZDDP is around 800 PPM in most "modern" oils.Supposedly new oil has an additive wear package to replace the missing ZDDP.......supposedly...
So how much ZDDP is required for an engine like the 4.0? Hi performance flat tappet cam grinders and the companies making high ZDDP specialty oils say between 1200 and 1600 PPM. Has Mopar issued a bulletin on ZDDP requirements?
And what is the normal service life of a 4.0? 250K miles on the average?




If I had a fresh engine for sure use a high ZDDP oil.

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2343717

Yes, but if its affordable and available then why not??? RotellaT 15w40s numbers are over 1000!!!

I typically use Amsoil AMO which is a full syn extended life 10w-40 oil with high levels of ZDDP.
Sometimes, if I do not get around to ordering oil on time. I go with a few different things depending on price.
Pennzoil Plat./Ultra, Valvoline Synpower, Rotella T6, Carquest 10w-40 full syn.

I haven't done any analysis on the CQ full syn to compare. But most of CQ's parts are high quality, so I doubt that the oil is much less. It is less expensive than other full syn.

CQ filters are made by Wix.

http://www.enginebuildermag.com/Article/98566/zddp_when_where_what_why_how.aspx

Good read on the engine builders view of API standards and ZDDP.

You can download the API standards, current and historical, from the American Petroleum Institute's website.

Wow. As in most of these oil/lube discussions, clear answers are hard to come by. I have been reading threads for a week now and have come to ZERO conclusions. It's amazing. I hear so much of "I hear Amsoil/Redline/XXXis good" but no one knows?. Which oils do you use?. And differential fluid, wow. No consensus at all (dana/chrys) not on brand/syn/visc. I guess I'll just keep using the mobil and get some 75w-90 syn for the front and rear diffs. I've read too many posts my head hurts..thx y'all

M7 98 has 192,000 miles, runs well, has 40+ psi oil pressure and gets fresh everyday dinosaur oil every 4,000 miles, whatever brand is on sale.

I am not convinced that ZDDP is needed, or that expensive oils have any benefits that justify the added expense.

YMMV

Tim_MN said:

M7 98 has 192,000 miles, runs well, has 40+ psi oil pressure and gets fresh everyday dinosaur oil every 4,000 miles, whatever brand is on sale.

I am not convinced that ZDDP is needed, or that expensive oils have any benefits that justify the added expense.

YMMV

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While I agree with you, I do not have the facilities to rebuild an engine...nor the ability......so again, I'm just being proactive with the RotellaT 15w40 from wally world but not springing for the T6 or even God forbid Amsoil or even Royal Purple.

Oil is important but just like guns, theres no magic bullet!

A heap with 200K with synthetic oil is still a heap with 200k on the clock.

About the only way to bring real data to these discussions is used oil analysis. And even then, all you can say is "Brand X leads to less wear in this motor compared to Brand Y" (you can get more specific than that, but still can't draw much else in the way of conclusions. Its also a good indication of the motor's condition).

Which is useful if all you want to know is which oil is "better" for a motor. The problem is that it's much harder to answer the question "Is Brand Y good enough for this motor?"

Everyone has different answers and plenty people have put 200K - 300K on these motors with nothing more than Tim's "whatever is on sale dino every 4K miles".

So I'm inclined to think it doesn't really matter unless you are trying to stretch your Oil Change Interval or have a rebuilt motor or high performance modification that is outside the original design specs of the motor.